U.S. Pat. No. 5,371,521 entitled Packaging Machine with Thermal Imprinter and Method (the "Teeter-Totter" patent) issued Dec. 6, 1994 to Rick S. Wehrmann and assigned to Automated Packaging Systems, Inc., the assignee of this patent, illustrates one application for thermal imprinters. That application is a schematically shown packaging machine which utilizes elongated chains of interconnected, preopened bags which are sequentially fed to a load station. As a web of interconnected, preopened bags is fed along a path of travel from a supply to the load station, the web passes a printing station. A thermal imprinter located at the printing station is utilized to imprint individual bags with information relative to the products being packaged, such as part numbers and instructions for use.
Thermal imprinters of the type shown in the Teeter-Totter patent utilize elongate printing foils or webs. Such a web is fed from a supply spool along a web path of travel through a printing station to a take-up mechanism which takes up spent printing foil. With prior machines when a workpiece is positioned at the printing station, the workpiece and printing foil are relatively fixed together for a printing operation. A printhead is then scanned along the web and energized at appropriate times in appropriate configurations to thermally transfer printing material from the web to the workpiece. When a workpiece is to be imprinted at spaced locations the printhead performs a printing operation at a first location and then it is moved relative to the workpiece and the web to the second location before it performs the second and spaced printing of information. The foil between the two printed locations is wasted because following the imprinting fresh foil is fed from the supply as the take-up draws in foil until the foil spanning the length of the printing station is fresh and unused. Obviously, such a procedure is wasteful. The procedure also adds considerable unneeded cost because the printing foils are quite expensive.
The procedures used with prior thermal imprinters have a further problem in that in many instances by the time the printing operation is completed the thermally transferred printing material has cooled and hardened. Accordingly, prior machines have been equipped with knife mechanisms for separating the foil from the workpiece following the printing operation. Not only does this obviously add cost and complexity to thermal printers, but it also degrades the quality of the printing from a level which might otherwise be achieved because the separation may not effectively transfer all of the material intended to be transferred and may cause chipping and flaking of the transferred print material as well.